Two-stroke combustion engines using the additional air during the scavenging are previously known in the art. These engines reduce fuel consumption and exhaust emissions.
The flow rate of scavenging air and the air/fuel mixture is typically proportional. An air valve is therefore provided to the air channel for supplying scavenging air to the engine. The air valve is operated in coordination with the throttle valve of the carburetor. The air valve and the throttle valve are commonly connected by a link mechanism, such as e.g. disclosed in U.S. Pat. No. 6,328,288 (FIGS. 3 and 4) and U.S. Pat. No. 7,503,292, or by engaging levers such as e.g. disclosed in U.S. Pat. No. 6,328,288 (FIG. 5) and U.S. Pat. No. 7,377,496. The connection between the throttle valve and the air valve can be a lost motion coupling allowing an opening range of the throttle valve in which the air valve does not open.
When the carburetor is provided with a choke valve, a cold start-up is performed by having the choke valve closed and the throttle valve is slightly opened. At this time, the air valve must be closed.
In U.S. Pat. No. 7,503,292 the opening state of the air valve is delimited by a choked state of said choke valve regardless of the throttle valve opening state by interaction with an air valve lever air valve axle and a choke valve lever of the choke valve axle.
U.S. Pat. No. 7,377,496, U.S. Pat. No. 6,928,996, U.S. Pat. No. 7,104,253 are other examples of carburetors sing scavenging air.